This invention relates to the field of voltage controlled functions and, more particularly, to circuits providing dual independent frequency response control for audio circuits.
It is well known in the art of audio devices that two characteristics are considered necessary by audio system purchasers and users. One is the ability to adjust bass and treble boosts to suit the user's aural taste. The other is the need to boost at least the bass frequencies as the volume control is turned down to compensate for the decreased sensitivity of the human ear at lower audio levels. The problem in the past has been to provide both these characteristics at the same time, but independently. In earlier circuits it was possible to accomplish the dual range control with audio devices having separate rotary potentiometers controlling volume, bass, treble and balance with simple RC networks which could be switched into each circuit to add the "loudness" function. With the increasing use of new IC's which include, on one chip, all of the four above-mentioned functions, coupled to merely rotary controls, it is no longer a simple matter to provide independent controls along with optimum loudness contour. Many attempts have been made to provide for varying contours, but in most instances the "loudness switch" merely brings the bass boost or bass and treble boosts up to a fixed value regardless of the volume control setting.